Abstract

This paper proposes a prudent implementation of robust pipeline in the domain of watermark based secure medical image transmission. The pipeline comprises of three stages, involving insertion of first watermark in the first stage and the second watermark in the second stage. Insertion of the watermark invokes a multi transform algorithm implemented in two steps. The first step is the application of Two-Way Arnold Transformation (TWAT) which scrambles the pixel locations in the source image, based on the number of cycles passed as one of the arguments to it, leading to a reduction in spatial correlation. The second step is 2-D Wavelet Transformation (WT) applied to the scrambled pixels that exploit the reduced correlation feature to generate the large values of coefficients. These large coefficient values can efficiently accommodate the wavelets coefficients of the inserted watermark. This step is a novel contribution compared to the existing models. Subsequently, the inverse WT is applied which concludes the first stage of the pipeline. The second stage of the pipeline also implements the same sequence of steps as that of the first stage but with the second watermark. In the final stage of the pipeline, the inverse TWAT is applied twice the number of times to the forward transformations applied in the first two stages. The entire pipeline is termed as Multi Transform based Robust Dual Water Marking (MTRDW). The pipeline is implemented on benchmark images with patient information and hospital logo as watermarks. The claimed features of the model are presented through computing the quality metrics such as SSIM, NCC and PSNR from the experiments conducted.

Introduction

The Information technology applications in biomedicine are combined with the hospital environment medical data resulting into online dispensary which is also known as telemedicine [1]. As a natural consequence, maintaining the confidentiality, integrity and robustness of data on the Internet against the various malicious attacks has become a complex task [2-4]. In the scenario of Networked Hospitals [5-11], exchanging medical information among the hospitals is a common phenomenon. Medical information (informatics) is generally presented in the form of images [12-13]. Medical Imaging is a process of creating images of the parts of the human body for the purposes of prognostic diagnosis purpose [14]. Medical imaging techniques such as endoscopy, cardiology, radiology, ultrasound scan etc. are used to study the functioning of various parts of the human body. Telemedicine and image processing reduce the difficulty involved in exchanging medical images among hospitals manually. But, the distribution of medical information over the Internet poses a threat of illegal use of the information. Therefore, the security of medical image is a prime goal of medical image processing. Digital watermarking [15-16] techniques are used for providing the security [17] to any medical image which is commonly referred to as the cover image. Digital watermarking is a process of embedding some extra piece of information (watermark) which can be easily retrieved and compared with the original information to assess the authenticity of information. This technique is widely used for adding authentication information and provides additional security without affecting the contents of the cover image. Many researchers have proposed various digital watermarking techniques that are classified based on various parameters such as watermarking domain, type of document on which watermark is applied, human perception (vision and speech) and the applications. Broadly speaking there are two types of watermarking techniques: Visible and Invisible. Visible watermarking techniques render the watermark signal to be clearly visible in the cover image to mark the ownership of the content. The invisible watermarking inserts the watermark in such a way that it is not visible to the human eye.

Conclusion

The present work describes the concept of dual watermarking. The cover medical image was dual watermarked maintaining high robustness. The two different types of invisible watermarks used were the robust watermarks HLOGO and PID. The process started by applying TWAT to medical images followed by DWT and their inverse. The major part of the work involves the insertion and extraction of invisible watermarks and the outputs were tested by applying different attacks to the output images. The experimental results show the good quality watermarked images. And when attacks are applied, retrieved watermarks were not remarkably degraded. The above findings are evident from the values of the image metrics PSNR, SSIM and NCC.